Cooling System: Thermostat
The thermostat is a coolant flow control component. Its purpose is to help regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element (4). The element connects to a valve (2) through a small piston (1). When the element is heated, it expands and exerts pressure against the small piston. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.
When the coolant temperature is below the rated thermostat opening temperature, the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up. After the coolant temperature reaches the rated thermostat opening temperature, the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.
The thermostat begins opening at 82° C (179° F). The thermostat fully opens at 95° C (203° F). The valve lift when the thermostat is fully open measures at least 8 mm (0.31 in).
An air bleed valve (2) is provided in the top of the thermostat. The air bleed valve vents any gas or air that has entered the cooling system.